There don't seem to be any indications that her abilities are anything other than natural.
Winter's organizational abilities are augmented by the young woman's
perfect memory. She can remember whole conversations verbatim, as well
as events, times, places, dates, faces, bits of trivia, and anything
else that passes before her senses. To her, these memories are like
holo-recordings that can be recalled instantly and in total detail. If
she experienced it, she can remember it—with every sound, smell,
sight, taste and touch intact. Currently, as Leia's aide in the
Provisional Council, Winter sits silently beside her Princess and
effectively records every word said. Due largely to this unusual
ability, Winter was instrumental in the search for "Delta Source," the
leak in security in the Imperial Palace on Coruscant.
Thrawn Trilogy Sourcebook
And from the old Star Wars Character Databank, her abilities are described as a "talent" and a "gift", implying that they're not artificially induced.
As the Organa family became involved in the growing Rebellion to
oppose the Empire, Winter's special talents were invaluable. Winter
has a holographic and audiographic memory: she forgets nothing she
sees or hears. Bail Organa assigned Winter to the Rebellion's
Procurement and Supply division. She was off-planet when the Empire
Winter's gift became a silent curse as she can never shake the
memories of her departed friends and destroyed world. She rarely lets
her feelings show, though at times, in private, her grief is almost
too much to bear. Her rigid control over her emotions and her
no-nonsense approach to her duties have caused some to comment that
her name befits her icy personality.